1. Field of the Invention
The present invention relates to a continuous paper treating apparatus such as an electrophotographic printer used for printing desired images on continuous paper. The present invention also relates to a tractor which is incorporated in a continuous paper treating apparatus for transferring the continuous paper.
2. Description of the Related Art
Referring FIG. 8, the outline of a conventional electrophotographic printer will be described. As illustrated, the conventional printer includes two tractors 2, a photosensitive drum 12, a transfer unit 13, a fixing unit 19, a scuff roller 16 and a pinch roller 17.
The tractors 2, being spaced from each other widthwise of the paper P, are provided for transferring continuous paper P toward the photosensitive drum 12. One of the tractors 2 is arranged adjacent to a longitudinal edge of the paper P, while the other tractor is arranged adjacent to the other longitudinal edge of the paper. Each tractor 2 includes a tractor belt 21 provided with a plurality of tractor pins 22 (the tractor belt 21 may be replaceable with rollers). When the tractor belt 21 is driven, the tractor pins 22 will come into engagement, one after another, with indexing holes formed in the paper P along the longitudinal edge thereof.
For performing printing, electrostatic latent images are formed on the photosensitive drum 12 by an image forming unit 14. The latent images are developed by a developing unit 15 to produce visible toner images. The toner images are transferred onto the paper P by the transfer unit 13, and then fixed by the fixing unit 19. Thereafter, the paper P is moved forward (downstream of the transfer path) by the scuff roller 16 and the pinch roller 17.
To obtain high-quality printing results, the longitudinal paper P needs to be properly tensioned while it is being transferred toward the photosensitive drum 12. Conventionally, necessary tension may be exerted by causing the circumferential speed of the drum 12 to be slightly greater than the paper transfer speed by the tractors 2. In this way, the paper P tends to be pulled more toward the drum 12 than toward the tractors 2, whereby required tension is generated in the paper.
As stated above, the paper P is pulled downstream due to the different operational speeds of the drum 12 and tractors 2. It is known, however, that there is another factor to cause the paper P to be pulled downstream. Specifically, in transferring toner images from the drum 12 to the paper P, the paper P tends to stick to the drum 12. As a result, the paper P, being caught temporarily by the drum 12, will be dragged downstream to a greater extent than is expected only from the effect of the above-mentioned speed difference.
In view of the additional pulling force acting on the paper P, the conventional apparatus may be disadvantageous in the following respects.
When the pulling force generated due to the sticking of the paper P is small enough, the paper P will be properly transferred along the predetermined path. However, when the pulling force becomes unacceptably large (this may happen, for example, when the temperature and/or humidity of the surface of the drum 12 are low), the paper P may unduly come off the tractor pins 22 of the tractors 2 or even be torn at the indexing holes of the paper P.
What makes the matters worse is that the paper P can adhere to the drum surface not only when the toner images are transferred to the paper P, but also after the paper P is moved downstream from the drum 12 (see an arrow N shown in FIG. 8). Such a phenomenon is often observed when the rotational speed of the drum 12 is increased, or when the thickness of the paper P is reduced. If this happens, the paper P will be pulled downstream much more strongly, which is clearly disadvantageous for performing proper printing.
Another type of conventional printer (not shown) may include two or more photosensitive drums for performing printing on both sides of continuous paper. In this printer, continuous paper may disadvantageously be pulled more forcibly by the plural photosensitive drums during a printing operation.
For addressing the problem of premature disengagement of the paper, conventionally use has been made of e.g. a tractor lid arranged above a tractor belt. However, the conventional tractor lid is configured to allow the presence of a clearance between the lid and the paper, thereby failing to prevent the premature disengagement of the paper. Also, the conventional lid cannot serve as effective countermeasures against the breakage of the paper.
The present invention has been proposed under the circumstances described above, and its object is to provide effective means for properly transferring continuous paper without causing the paper to be torn at indexing holes or to unduly come off paper tractors.
According to a first aspect of the present invention, there is provided a continuous paper treating apparatus comprising:
a tractor including a rotatable driving member provided with a plurality of tractor pins, the tractor also including a tractor lid for covering the driving member; and
treating means for treating continuous paper transferred along a predetermined path by the tractor;
wherein the tractor further includes a support member having a paper support surface for supporting the continuous paper, the tractor further including a presser member supported by the tractor lid in a manner such that the presser member is variable in position and posture relative to the tractor lid, the presser member having a pressing surface for pressing the continuous paper, the tractor further including urging means for urging the presser member toward the paper supporting surface so as to cause the pressing surface to press the continuous paper onto the paper supporting surface.
According to a preferred embodiment of the present invention, the urging means may be an elastic member such as a spring. In place of the spring, a rubber member may be used.
With the above arrangement, continuous paper (on the way to the treating means from the tractor) is pressed onto the paper supporting surface by the presser member. In this manner, a suitable frictional force is advantageously applied to the paper for balancing out unfavorable pulling force exerted by the treating means. As a result, it is possible to prevent the continuous paper from being torn at the indexing holes or unduly coming off the tractor.
Further, according to the present invention, the continuous paper is suitably held between the pressing surface of the presser member and the paper supporting surface. In this way, the paper is prevented from deviating from the predetermined paper transfer path, so that the tractor pins will be properly engaged with the indexing holes of the paper.
Still further, since the presser member is variable in position and posture relative to the tractor lid, the entirety of the pressing surface of the presser member can be brought into contact with the paper. Thus, desired frictional force is reliably applied to the paper.
Preferably, the tractor lid may be movable to be selectively brought into facing relation to the paper supporting surface. Further, the tractor lid may be urged toward the paper supporting surface with a first urging force, while the presser member may be urged toward the paper supporting surface with a second urging force which is greater than the first urging force.
With such an arrangement, not only the presser member but also the tractor lid prevents the continuous paper from unduly coming off the tractor
Preferably, the tractor lid may be movable into facing relation to the paper supporting surface, and this facing relation may cause the tractor lid and the paper supporting surface to define a clearance when the continuous paper is unsupported by the paper supporting surface.
With such an arrangement, the continuous paper is easily inserted between the tractor lid and the paper supporting surface.
Preferably, the driving member may comprise a tractor belt from which the tractor pins protrude. Advantageously, at least two of the tractor pins may be present upstream of the paper transfer path from the presser member.
Preferably, the presser member may be provided with a chamfered portion defining a paper inlet opening for inserting the continuous paper between the pressing surface and the paper supporting surface.
According to a second aspect of the present invention, there is provided a tractor for transferring continuous paper comprising:
a rotatable driving member provided with a plurality of tractor pins;
a tractor lid for covering the driving member;
a support member having a paper support surface for supporting the continuous paper;
a presser member supported by the tractor lid in a manner such that the presser member is variable in position and posture relative to the tractor lid, the presser member having a pressing surface for pressing the continuous paper; and
urging means for urging the presser member toward the paper supporting surface so as to cause the pressing surface to press the continuous paper onto the paper supporting surface.
The tractor of the present invention may advantageously be incorporated in a continuous paper treating apparatus, such as an electrophotographic printer, for transferring continuous paper.